In clocks, pendulums, and mechanical or electronic watches, there is always a regulator organ making it possible, as its name indicates, to regulate the running of the timepiece. In the case of a mechanical watch, the regulator organ is formed by a balance and a spiral spring.
Traditionally, the spiral is a leaf, in general metal, with a rectangular section wound on itself in the shape of a spiral of Archimedes. It is fixed in its center on the balance-staff, by a piece called a collet. The outside of the spiral is fixed to a balance, called balance-cock, by a piece called a balance-spring stud. The balance-spring stud is fixed either directly to the balance-cock, or via a mobile balance-spring stud support.
Such an assembly of a spiral is not optimal for the isochronism of the watch. In fact, the center of the spiral moves during its development, which causes reaction forces at the pivots of the balance-staff. The intensity of the forces exerted on the pivots participate greatly in the isochronism that is generally observed.
Timepiece are known provided with two spirals mounted on the balance-staff, in opposite directions, arranged in different planes. The house H. Moser & Cie offers an escapement provided with two spirals arranged on either side of the balance, in opposite directions. Document EP2063325 proposes a mechanism with two traditional spirals arranged concentrically and coplanarly. It is known that it is difficult to obtain precise characteristics for spirals made traditionally and that therefore, two spirals will most often be different, even just slightly. Thus, the adjustment of such a balance provided with two spirals having different characteristics, and the alignment of the forces exerted by the two spirals, present difficulties. Furthermore, the likely difference between the two spirals makes the result of the forces exerted at the balance-staff, in most cases, non-null and difficult to control.
The present invention therefore aims to propose a spiral making it possible to improve the isochronism of a watch, while remaining simple to implement.